371
FXUS02 KWBC 281933
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
333 PM EDT Mon Sep 28 2026

Valid 12Z Thu Oct 01 2026 - 12Z Mon Oct 05 2026


...Major Multi-day South-Central to East-Central U.S. Excessive
Rainfall/Flooding threat fueled by moist tropical connections...


...Guidance/Predictability Assessment...

The latest guidance remains generally agreeable on the overall
synoptic pattern late week and into the weekend featuring an
energetic northern stream and a lingering southern-stream upper-low
over the southwest to south-central U.S. The upper-low will begin
to weaken/transition into an open wave and become absorbed within
the northern stream as a northerly cold front catches wavy frontal
boundaries over the south-central U.S. Thereafter, the main
question in the forecast becomes the speed of system progression.
The deterministic guidance has trended a bit slower with the
frontal progression late week/early weekend with this initial
system, with the front generally tending to hang a bit further
north through the Ohio/Tennessee Valleys into the Carolinas and
Mid-Atlantic compared to the prior forecast as upper-ridging builds
in a bit stronger over the Southeast. On the other hand, the
guidance has trended faster with another system upstream along the
northern tier of the U.S. late weekend/early next week with a
second sweeping cold front spreading across the central and then
eastern U.S. The deterministic guidance is the most progressive
with this system compared to the means. Not surprisingly, the
positioning of the frontal boundary early in the period and the
approach of the second boundary late in the period will impact the
location and coverage of what is expected to be a prolonged period
of heavy rainfall from the south-central to eastern U.S. Felt the
13Z NBM provided a good compromise solution QPF-wise, showing some
more significant adjustments to match the trends in the
deterministic guidance early in the period with the slower trending
front, while matching the footprint in the means later in the
period when uncertainty increases. The updated WPC forecast overall
followed a similar trend, beginning with a composite blend of the
best clustered deterministic guidance early in the period before
shifting towards the EC/GEFS means later in the period as spread
with frontal progression increases.


...Pattern Overview and Weather/Hazards Highlights...

A closed upper trough/low with wavy frontal systems will shift
slowly eastward from the Southwest U.S. to the South-central U.S.
mid-later week in southern stream split flow. Widespread excessive
rainfall/flooding threats over the Southwest/Southern Rockies
states during the short range will then focus over the South-
central U.S. then East-central/Southern U.S. as further focused by
Gulf/Southeast Coast frontal genesis. This event will be fueled by
a tropical moisture connection from current East Pacific Hurricane
Polo forecast to weaken with landfall/track across Baja California
and Northwest Mexico over the next couple of days. There will also
develop an increasingly deep and protracted lead Gulf inflow
pattern with tropical influence. This expansive multi-day threat
should prove slow to progress late week/next weekend wedged between
upper ridges over the Southwest and Southeast U.S..

Accordingly, the WPC Excessive Rainfall Outlook (ERO) offers
anomalously large Marginal and Slight Risk areas from the South-
Central to East-central U.S. on Day4/Thursday and Day 5/Friday. The
Day 4 also includes a Southern Plains Moderate Risk. Activity will
progress slowly from the East-central U.S. to the East later
period with the greatest confidence in additional heavy rainfall
shifting from the Southern Plains/Middle Miss Valley to the
Tenn/Lower Miss Valleys, as well as possibly into the northern Mid-
Atlantic. These EROs and supporting WPC Hazards Outlook areas are
all linked below.

Meanwhile, systems within a more progressive/zonal mean northern
stream flow will support passage of a series of wavy frontal
systems across the U.S. northern tier of the nation from the
Northwest through the Northeast this week. These will act to
provide a northern rainfall shield focus and over-running for
lifting moisture/clouds and deliver moderating post-frontal fall
temperatures to spread/sink southward with high pressure settling.
Persistent upper-ridging will lead to a period of above-average
temperatures over much of the western U.S. including highs into the
90s and low 100s for central/southern California and the Desert
Southwest. Some of this heat may reach hazardous levels for
southern California this weekend.

Putnam/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw






















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